Projection screens for the display of pictures are well known in the art. Most of the screens have traditionally had a material on the surface thereof for the dispersion of light incident thereon, such as from a projector, in a multitude of directions.
As described in my prior U.S. Pat. No. 3,782,805, previous attempts have been made to direct light upon the screen from the projector into a predetermined viewing area. Thus, in my prior patent, No. 3,712,708, a lenticular projection screen is disclosed consisting of a plurality of overlapping spherical concave lenses formed in reflective material. Therein, the lenses in the screen are constructed so that the projected light rays are reflected to predetermined viewing areas in front of the screen.
When such screens are made of a reflective material, problems of reflections from sources other than the projector obviously arise. While these can be overcome by operating in a dark room, even in such a case extraneous light sources are always a problem. In addition, while attempts have been made to put light absorbing elements in predetermined locations with respect to the reflective material in the screen, such attempts have added additional annoyance to the use of the screen and/or additional costs thereto.
As discussed in my U.S. Pat. No. 3,782,805, U.S. Pat. No. 1,610,423 to Cawley shows a daylight projection screen in which the transparent material is shaped to have prism-like ridges on the back thereof for reflecting light incident thereon from a predetermined angle. Cawley, however, teaches that the critical angle of the material used should be as close to 45.degree. as possible, that the angle of the sides of the prism-like portions should be inclined with respect to the plane of the material at 45.degree.. In this manner, the Cawley projection screen reflects only light incident upon the screen from a single direction back towards the audience with all other light passing therethrough. Thus, if the audience is not located directly in front of the screen, or if the screen is moved by a slight angle with respect to the incoming projected light, the image reflected back to the audience is lost. Similarly, this results if the audience is not sitting in its precise angular relationship respecting the screen.
In my U.S. Pat. No. 3,782,805, I therefore taught a projection screen which efficiently uses the light provided by the projector, but does not reflect undesirable images to the audience and is viewable from positions other than directly in front of the screen. The projection screen thus taught in my patent has proved to be extremely significant, and has demonstrated remarkable results with respect to the ability to reflect back to the audience only light incident upon the screen from a small predetermined angle, while permitting light from outside that angle to pass therethrough.